Fix atlas alerts with pint

[QuentinBisson]

Before adding a new alerting rule into this repository you should consider creating an SLO rules instead.
SLO helps you both increase the quality of your monitoring and reduce the alert noise.

• How to create a SLO rule: https://github.com/giantswarm/sloth-rules#how-to-create-a-slo
• Documentation: https://intranet.giantswarm.io/docs/monitoring/slo-alerting/

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Towards: giantswarm/roadmap#3318

This PR fixes atlas alerts with pint

Checklist

• Update CHANGELOG.md
• Add Unit tests
• Follow Alert structure
• Consider creating a dashboard (guidelines) (if it does not exist already) to help oncallers monitor the status of the issue.
• Request review from oncall area, as well as team (e.g: oncall-kaas-cloud GitHub group).

[hervenicol]

LGTM.

2 remarks:

• that's not a lot 😁
• the pint-aggregations target does more than aggregations. But I'm not sure I should update this, as the errors is fires make sense.

[QuentinBisson]

I quite like pint-aggregations for now and we later enforce the full one :)
There are a few more that i'll try to fix but they requires rewriting the alerts a bit more because they use absent IIRC

[QuentinBisson]

@hervenicol do you want to take another look with the remaining changes?

[hervenicol]

LGTM.